The use of mold inserts in the thermoforming manufacture of plastics is not new. Having these inserts movable in relation to their position within a cavity for the purpose of drawing heated thermoformed plastic over the cavity and drawing it within the cavity against the mold insert is also not new.
U.S. Pat. No. 6,939,504 that issued to Homann et al, on Sep. 6, 2005, describes cavity mold inserts that are moveable to allow for plastic materials to fill the entire article defining the mold cavity. The article is formed, cooled then removed from the cavity. The present invention incorporates an internally moving portion of the insert surface that will retract after the article is cooled. This retraction of an area of the cavity surface allows the article to be removed or stripped from the thermoforming cavity insert with greater ease and efficiency, improving the run time of the overall thermoforming process.
A self-stripping forming insert comprising in combination; stationary portion and a movable portion. The stationary portion has a top surface, a bottom surface, an inside surface, an outside surface, a spring mechanism and more than one vacuum passage. The stationary portion has a plurality of openings through it from the top surface to each vacuum passage. The stationary portion houses the movable portion.
The movable portion has a top surface, a bottom surface, an outer edge, a plurality of openings through it. The top surface has male protrusion extending from the top surface. The top surface also has female intrusions depending from the top surface. The top surface may have a combination of male protrusions extending from and female intrusions depending from the top surface. The bottom surface is generally flat. The outer edge of the insert defines the outer circumference of the movable portion of the insert.
The spring mechanism is internal to the stationary portion and is attached to the movable portion through the bottom surface of the movable portion. The spring mechanism is vacuum controlled and mechanically activated moving the movable portion in an up and down motion, relative to the bottom surface, much like an automobile piston.
The opening through the movable portion extends from said top surface of the movable portion through to the bottom surface of the movable portion, said openings allowing a vacuum to be activated upon the top surface of the forming insert drawing molten plastic into and over the forming insert.